President-elect Barack Obama yesterday promised an extraordinary multibillion-dollar economic package to deliver a jolt to the US and stave off what he described as a "crisis of historic proportions".

Obama, introducing his new economic team of Tim Geithner as treasury secretary and Larry Summers as his White House economics adviser, stressed that the scale of the recession required action by the US in tandem with other governments. His team will reach out to other countries to coordinate efforts, he said.

Asked about speculation that his package will cost between $700bn (£460bn) and $1tr, Obama declined to put a figure on it. He said it was necessary not only to have a thriving Wall Street but a thriving main street too. "We are going to do what is required to jolt this economy back into shape," the president-elect said.

Speaking at a press conference in Chicago, Obama signalled that he is moving at speed to try to reassure nervous markets as well as the public. His team would begin work straight away. "We do not have a minute to waste," he said.

It was a confident performance that contrasted with a short, stumbling appearance by President George Bush in Washington hours earlier to confirm federal help for the Citigroup bank.

Bush hinted at more bail-outs if necessary. "This is a tough situation for America, but we'll recover from it," he told reporters. "The first step to recovery is to safeguard our financial system."

But the outgoing president undermined confidence that he was on top of his brief by referring to Citigroup as Citicorp, the name it has not used for a decade. The White House later issued a clarification.

Obama, who was phoned by Bush yesterday to discuss the Citigroup bail-out, plans another press conference today on the economy. It is intended to partly address the big question arising from his stimulus package: how to pay for it. The US faced a deficit next year, even before the extra spending he proposed yesterday.

Obama made a point when introducing Geithner, president of the New York Federal Reserve Bank, of highlighting his international experience. "The reality is that the economic crisis we face is no longer just an American crisis, it is a global crisis - and we will need to reach out to countries around the world to craft a global response. Tim's extensive international experience makes him uniquely suited for this work," Obama said.

Obama, who also announced that Christina Romer, a professor at the University of California, is to head his council of economic advisers, said his team shared his basic belief that "we cannot have a thriving Wall Street while main street suffers". He said he wanted to create 2.5m jobs.

The president-elect claimed there was a consensus among liberals and conservatives on the need for a huge stimulus package. He said he intended to push ahead with tax reforms that would see higher costs for those earning more than $250,000 a year. The tax cuts would help stimulate the economy, he added. "It is important if we're going to help pay for some of these expenditures that are absolutely necessary to get our economy back on track that those who are able to pay a little bit more do so," he said.

The president-elect sent a warning to America's struggling carmakers, who want the federal government to bail them out. The carmakers angered members of Congress last week when they turned up without a detailed plan for revitalising the car industry.

Obama, who a fortnight ago called on Bush and the Congress to help carmakers, sided yesterday with congressional leaders. "We cannot just write a blank cheque to the auto industry," he said.